Amblyopia, commonly known as lazy eye, is one of the most common causes of visual impairment in children. The majority of the clinical investigations attribute amblyopia to the brain's preference for a dominant eye over a weak eye. The condition often persists into adulthood and bears the risk of bilateral vision impairment and even blindness. In fact, amblyopia has been reported as the leading cause of vision loss in one eye for the 20-70 year old age group, indicating a need to improve detection as well as treatment for the condition.
When diagnosed in children, the condition has traditionally been treated with occlusion therapy that excludes or reduces the vision in the dominant eye. Occlusion therapy typically requires the patient to use an eye patch that completely or partially covers the dominant eye. Compliance with occlusion therapy, however, has been problematic because the patients are typically no older than the age of seven. These young patients are unlikely to comply with the therapy for a number of reasons including personal distaste, skin irritation, cosmetic embarrassment, and other social and psychological factors.
An alternative treatment that has been relied upon to treat amblyopia is therapy using a cycloplegic drug known as atropine. Atropine functions by dilating the pupils and blurring the image seen through the dominant eye. Atropine addresses the low compliance rate for occlusion therapy but drug therapy progresses slower than occlusion therapy and paralyzes a key optical function in the dominant eye for an extended period of time.
Although occlusion therapy and atropine may improve visual acuity for patients, the visual gains are not guaranteed to remain stable and often regress when therapy ceases. Further, until a recent National Eye Institute study was published showing that many children from age seven through 17 with amblyopia may benefit from treatment, it was commonly believed that amblyopia is untreatable for anyone beyond the age of seven. Therefore, neither occlusion therapy nor atropine has been effectively used to treat patients over the age of seven.
In a human eye, there are six external muscles that move both eyes together in synchronized motion. Ocular deviation occurs when one or both eyes do not move normally, causing abnormal visual reception. As a result, a patient may experience one or more symptoms or visual impairments including diplopia where the patient has double vision or strabismus, also known as “cross-eyes,” where the patient's eyes do not look at the same point at the same time. Ocular deviation may result from ocular or neurological damage including ocular nerve palsy, vascular disease, thyroid disease, multiple sclerosis, myasthenia gravis, traumatic brain injury, stroke, facial fracture, or eye trauma.
Although a majority of patients whose condition results from trauma such as brain injury or stroke recover within 12 months, proper vision assistance is critical to recovery. Traditional therapies for ocular deviation include patching one eye to eliminate the image received in that eye and rendering the patient monocular, and using prisms to fuse the images received by both eyes. Patching, however, may be uncomfortable and causes cosmetic concerns. Prism, on the other hand, can create other problems such as eye strain when the prismatic lenses used are improperly adjusted or unstable.
Binocular vision (binocular refers to two eyes) is the result of the alignment of the eyes and the unification of their respective views of the environment. Binocular vision provides depth evaluation and stereoscopic vision. The binocular vision could be affected by deficiencies such as, amblyopia (or, reduction of vision in one eye), strabismus deviation of one eye, diplopia (or, a condition where a single object is seen in double), accommodation deficit (or, a condition where the eye is not able to obtain clear image of near object), and/or convergence and fusion insufficiency (or, inability to maintain superimposition of 2 images).
In addition to providing stereopsis and an improved field of vision, benefits of having good binocular vision include the ability to perform advanced visual tasks. Binocular weaknesses such as convergence and fusion insufficiency (inability to maintain superimposition of 2 images) reduce visual performance.